The invention relates generally to stators for use with progressive cavity pumps or motors. More specifically, to a resilient material lined stator and a method of forming the stator.
Progressive cavity pumps or motors, also referred to as a progressing cavity pumps or motors, typically include a power section consisting of a rotor with a profiled helical outer surface disposed within a stator with a profiled helical inner surface. The rotor and stator of a progressive cavity apparatus operate according to the Moineau principle, originally disclosed in U.S. Pat. No. 1,892,217.
In use as a pump, relative rotation is provided between the stator and rotor by any means known in the art, and a portion of the profiled helical outer surface of the rotor engages the profiled helical inner surface of the stator to form a sealed chamber or cavity. As the rotor turns eccentrically within the stator, the cavity progresses axially to move any fluid present in the cavity.
In use as a motor, a fluid source is provided to the cavities formed between the rotor and stator. The pressure of the fluid causes the cavity to progress and a relative rotation between the stator and rotor. In this manner fluidic energy can be converted into mechanical energy.
As progressive cavity pumps or motors rely on a seal between the stator and rotor surfaces, one of or both of these surfaces preferably includes a resilient or dimensionally forgiving material. Typically, the resilient material has been a relatively thin layer of elastomer disposed in the interior surface of the stator. A stator with a thin elastomeric layer is typically referred to as thin wall or even wall design.
An elastomeric lined stator with a uniform or even thickness elastomeric layer has previously been disclosed in U.S. Pat. No. 3,084,631 on “Helical Gear Pump with Stator Compression”. The prior art has evolved around the principle of injecting an elastomer into a relatively narrow void between a stator body with a profiled helical bore and a core, or mandrel, with a profiled helical outer surface. The core is then removed after curing of the elastomer and the remaining assembly forms the elastomeric lined stator. The elastomer layer is essentially the last component formed.
The stator bodies mentioned above have a pre-formed profiled helical bore. The profiled helical bore is generally manufactured by methods such as rolling, swaging, or spray forming, as described in U.S. Pat. No. 6,543,132 on “Methods of Making Mud Motors”, incorporated by reference herein. Similarly, a profiled helical bore can be formed by metal extrusion, as described in U.S. Pat. No. 6,568,076 on “Internally Profiled Stator Tube”, incorporated by reference herein. Further, various hot or cold metal forming techniques, such as pilgering, flow forming, or hydraulic forming, as described in P.C.T. Pub. No. WO 2004/036043 A1 on “Stators of a Moineau-Pump”, incorporated by reference herein, can be used to form a stator body with a profiled helical bore.
A stator body can also be formed by creating a profiled helical bore in relatively thin metal tubing. This formed metal tube can then be used as the stator body by itself, with an injected inner elastomeric layer, or the formed metal tube can be inserted inside into a second body with a longitudinal bore to form the stator body. A stator body with a profiled helical bore can also be formed through other process such as sintering or hot isostatic pressing of powdered materials, for example, a metal, or the profiled helical bore can be machined directly into a body.
The prior art designs lead to several inherent manufacturing problems when lining the profiled helical bore of the stator with an injected or molded elastomeric layer, for example, rotational and lateral misalignment. Rotational misalignment can occur when the apex of a lobe of a stator and the apex of an adjacent lobe of the core are not substantially aligned relative to a radial line extending from the central axis during the elastomer injection step. The rotational misalignment caused by not appropriately matching the profiles of the core (not shown) and the inner bore of the stator 120 is shown in FIG. 1. The result is a loss of control of the elastomer 100 thickness on both sides of a lobe 102. One side 104 of each lobe has an elastomeric layer thicker than intended and the other side 106 of each lobe has an elastomeric layer thinner than intended.
Another obstacle to forming a desired thickness of an elastomeric layer in a stator is lateral misalignment of the core (not shown) and the stator, shown in FIG. 2. When forming an elastomeric layer 200, there can be lateral misalignment of the profiled helical bore of the stator body 220 and the core (not shown). For example, in a long stator there can be lateral misalignment at the mid section even when the ends of the stator body 220 and the core are aligned properly due to a sagging of the core and/or the stator body 220. Lateral misalignment during the elastomer injection step creates a loss of control of the elastomer 200 thickness in the profiled helical bore, where one side 204 of the bore has an elastomeric layer thicker than intended and the other side 206 of the bore has an elastomeric layer thinner than intended.
One potential solution that has been attempted to solve the lateral alignment problem is the use of radial alignment pins and/or screw plugs passing through the stator body 220 to support the core during the elastomer molding step. However, this typically resulted in another failure mode with fluid leaking through those holes and/or plugs in the stator when used as a progressive cavity apparatus.
It is also desirable to have a conduit, a conductor, and/or a pathway extending through the stator. The conduits, conductors, and/or pathways can be used for communicating in electrical, hydraulic and/or mechanical form between the two ends of the stator. One such implementation is covered in U.S. Pat. No. 5,171,139 on “Moineau Motor With Conduits Through The Stator” which discloses conduits that are embedded within the elastomeric layer of the stator. However, embedding a conduit within the elastomeric layer can limit the size of conduit used when a thin elastomer layer is desired or create other complications.